Recently, a recording and reproducing apparatus has been developed the body of which has a cartridge holder for housing a disk cartridge and an opening for allowing insertion of the cartridge into the body. More specifically, the cartridge which is molded out of a hard material and holds a magnetic disk rotatably is inserted into the body through the opening, and then it is received in the cartridge holder in the body. Eventually, the cartridge is operatively connected with the apparatus for effecting recording or reproduction. The aforementioned opening of this apparatus is covered with a shutter to prevent dust from intruding into the body of the apparatus. The cartridge holder is required to be disposed near the opening through which the cartridge is inserted such that the cartridge is guided by the holder while it is being inserted. In order to place the cartridge in position within the apparatus, the shutter is first opened. Then, the cartridge is inserted into the cartridge holder. Thereafter, the holder must be brought into operative condition. At this time, the operation for opening the shutter may initiate movement of the cartridge holder, if the shutter makes contact with the holder.